1. Field of Invention
The present invention relates to a semiconductor gap-filling layer and a method of fabricating the same. More particularly, the present invention relates to a silicon nitride gap-filling layer and a method of fabricating the same.
2. Description of Related Art
With the development of technology on electronic equipments for communication, etc., the operating speed of a transistor increases rapidly. However, limited by the mobility of electrons and holes in a silicon channel, the area of application of a transistor is limited.
Altering the mobility rate of electrons and holes in the channel by controlling the mechanical stress in the channel is one approach to overcome the limitations generated from the miniaturization of a device.
The application of silicon nitride as a contact etching stop layer (CESL) has been proposed for generating strain to influence the driving current and ion gain of a transistor; and thus improving the efficiency of the device. This type of technique is known as localized mechanical stress control.
The strain of a contact etching stop layer is directly proportional to the stress and the thickness of the film layer. Accordingly, increasing the thickness and the strain of the film layer can respectively increase the strain of the contact etching stop layer.
The contact etching stop layer is formed after the fabrication of the silicide layer of the device is completed. However, the commonly used silicide (NiSi) is unable to endure a higher thermal budget. Therefore, the contact etching stop layer must be fabricated in a temperature below 550° C. However, the tensile stress of silicon nitride formed below 550° C. is inadequate. Accordingly, the tensile stress of a contact etching stop layer is typically improved by performing a curing process after deposition.
Regarding the approach of increasing the thickness of the contact etching stop layer, seam and void 100 as shown in FIG. 1, are easily generated due to the overly thick silicon nitride layer 102 and the insufficient gap-filling capability of the subsequently deposited dielectric layer 104. Consequently, problems of residues from contact etching or short circuit between contacts or between the contact and the gate are resulted. On the other hand, performing the curing process for enhancing the stress of the silicon nitride layer after the deposition process may result with problems of crack generated in the overly thick silicon nitride layer.